Mooring line fatigue: A risk analysis for an SPM cage system

In recent years, the development of single-point mooring (SPM) cage systems has received much attention due to their eco-friendly features. However, natural disasters such as hurricanes and typhoons can cause severe damage to the integrity of net cage system. To avoid mooring system failure, selecting an appropriate breaking strength for mooring lines is becoming an important issue in marine aquaculture industry. This study evaluates the failure risk of a mooring line based on extended-period environmental loadings. Results indicate that the recommended replacement period of a polyester (PET) mooring line (diameter 38 mm) is about 6.55 years if the line's safety factor is 1. However, if the required safety factor increases to 1.5 (diameter 50 mm), then the replacement period extends to 23.81 years about six times that of original life. The fatigue failure probability for mooring lines in the service period is about 0.49 and 0.29 for safety factors of 1 and 1.5, respectively.